IMPORTANT NOTE: This question was copied from POF following student feedback. However, it appears to be beyond the scope of the Performance syllabus. Please inform us if you encounter this question in your 032 Performance exam.

The airframe may become contaminated by ice, frost or water either whilst it is in flight or when standing on the ground.

HEAVY RAIN

Heavy rain has the following effects on aeroplane performance:

- The impingement and rapid accumulation of water sufficiently distorts the shape of the upper wing surface and diminishes the total lift by up to 30% of its normal value.
- The impact of the rain on an aeroplane in the landing configuration decreases the aircraft’s forward speed.
- When operating in such conditions a jet engine is slow to respond to rapid demands for thrust.
- The mass of the rain can increase the aircraft mass momentarily.

The total effect of these factors for any aeroplane experiencing such weather conditions is to produce a much lower level of performance. The mass increase raises the stalling speed, whilst the reduced lift and increased drag together reduce the forward speed achieved.

An additional consideration, while not affecting stall speed, is the effect of the impact of heavy rain on the aircraft. Momentum will be lost and airspeed will decrease, requiring increased thrust. At the same time, heavy rain will also be driving the aircraft downwards.